Method of controlling cell selection for a wireless communication system and related device

ABSTRACT

A method of controlling CSG, known as closed subscriber group, cell selection for a wireless communication system is provided. The wireless communication system includes a network and a user equipment including a whitelist capable of providing a list of accessible CSG cells. The method includes updating the whitelist when the user equipment subscribes to a CSG cell that is not included in the whitelist or does not subscribe to a CSG cell in the whitelist.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods and devices utilized in awireless communication system, and more particularly, to methods anddevices utilized in the wireless communication system for controllingcell selection.

2. Description of the Prior Art

A System Architecture Evolution (SAE) system, set forth by 3GPP (3rdGeneration Partnership Project) is a new core network architecture forUMTS (Universal Mobile Telecommunications System), addressingcost-efficient deployment and operations for mass-market usage of IPservices. The main network evolutions include meeting the targets for aradio-interface of a long term evolution (LTE) system, simplifiednetwork architecture, an All-IP Network, only packet switched means forall services, no circuit switching, and support for mobility and servicecontinuity between heterogeneous access networks, such as between 2G/3G,LTE, non-3GPP access systems.

The SAE core network includes an MME (Mobility Management Entity), anS-GW (Serving Gateway) and a P-GW (PDN gateway). The MME is a controlplane entity that manages the attachment to the network, theauthentication of the user equipment (UE), and interfaces an E-RAN(evolved radio access network) for the creation of relevant radiobearers.

Functions of the SAE include the Non-Access-Stratum (NAS) functions tobe performed by the UE in idle mode, the NAS signalling proceduresbetween the UE and an evolved packet core network (EPC) via an E-UTRAN(evolved UMTS radio access network) including eNBs (evolved Node-Bs),and layer 3 signalling procedures between the UE and the EPC vianon-3GPP access networks.

Under NAS functions, home cell deployments are defined as a single eNBused in a building or a small group of cells, e.g. in a campusdeployment. Access to home cells is restricted to particularsubscribers. In home cell deployments, a CSG (closed subscriber group)cell as part of the PLMN (public land mobile network) is only suitablefor a UE if an id of the CSG cell is in a whitelist of the UE. Coverageof the CSG cell may be home, building, campus coverage, etc. Thewhitelist is a list of CSG cell ids where the UE is allowed to camp.

For home cell deployments, two options A and B provide different usageof the whitelist. In addition, an attach procedure and a tracking areaupdating (TAU) procedure, are both EMM (EPS Mobility Management)specific procedures as part of the NAS signalling procedures, and can beused for updating the whitelist of the UE.

In the option A, a CSG area is defined as a tracking area (TA) thatconsists of a cell or group of cells to which access is restricted to adefined group of users. A single cell can only belong to one TA or oneCSG-TA. To achieve a concept of “registration to multiple trackingareas”, the MME can assign several TAs and CSG-TAs to the UE. As part ofthe attach and/or TAU procedures, the MME may provide the UE with one ormore TACs (TA cells) identifying a CSG or non-CSG tracking area. If theTA identifies a CSG, the UE adds this identity to the whitelist. The MMEindicates the UE whether or not a CSG, to which the UE is subscribed,belongs to a current registration area assigned to the UE, and if itdoes, the UE does not trigger the tracking area update when entering theCSG.

In addition, the MME checks if the CSG TA identifier belongs to the onessubscribed by the UE or not. If the CSG TA identifier does not matchwith the subscribed ones, the MME rejects the network access initiatedby the UE.

In the option B, a CSG area consists of a cell or group of cells towhich access is restricted to a defined group of users. A single cellcan only belong to one CSG area or one non-CSG area. To achieve aconcept of “registration to multiple tracking areas”, the MME assignsseveral TAs to the UE. The CSG cell area identity consists of a TAI+acell identity code. The list of allowed CSG cell area identities(whitelist) shall be stored in the UICC. The MME may provide thewhitelist in, for example, a similar way as today's Equivalent PLMN listor the tracking area list (e.g., acceptance message of theattach/tracking area updating procedures). The UE considers itswhitelist as valid until it receives a new list in the next EMMprocedure or it is commanded by the network to delete all entries in thewhitelist. The UE shall treat all CSG cells where the UE does not belongto the associated CSG as though they are NOT a suitable cell.

An eNB, which belongs to a CSG area, sends the CSG cell area identity,i.e., TAI plus (parts of) cell identity, to the MME wheneverauthorization needs to be checked in the MME. On receipt of a new causevalue the UE removes CSG cell area identity (outdated information) fromthe stored whitelist. This prevents non-allowed UEs from accessing cellsindicated as restricted.

In the option A, the whitelist consists of CSG-TAs, whereas thewhitelist in the option B consists of cell identities including TAs andcell Ids.

In the prior art, two problems of cell selection are described asfollows.

The first problem is that, in the option A or B, the whitelist isupdated by the attach or tracking area updating procedure. However, theattach and tracking area updating procedures can only be initiated bythe UE. The initiating criteria of the attach procedure is the UEattempting to enter an EMM-CONNECTED mode from the in an EMM-IDLE mode.The tracking area updating procedure is used for the following purposesof normal tracking area updating, periodic tracking area updating andintersystem change.

As can be seen from the above, the UE only initiates the attach ortracking area updating procedure when certain conditions are met. Thismeans the UE cannot initiates the attach or tracking area updatingprocedure anytime. Besides, the network only can update the whitelist ofa UE when the UE performs the attach or tracking area updatingprocedure.

The UE cannot access a new subscribed CSG cell immediately because theUE has to wait for completion of whitelist updating that adds this CSGcell to the whitelist through the attach procedure or tracking areaupdating procedure. Even the UE finds the new subscribed CSG cell is thebest cell for cell reselection, this CSG cell cannot be selected becausethis cell is not in whitelist.

The second problem is described as bellow. According to the prior art,the cell measurement and reselection rules for macro cell are appliedfor CSG cell as well. Besides, the user pays less money if the UEaccesses the service via the subscribed CSG cell than via a non-CSGcell. When a UE subscribed CSG cell, the UE camps on the macro cell andalso stays in coverage of a CSG cell deployed in coverage of the macrocell, the UE is not able to reselect this CSG cell when none of the cellreselection criteria is met or even the UE does not measure this CSGcell since measurement criteria are not met. In this situation, the UEcan only continue receiving service via the macro cells even though theUE has entered the CSG cell coverage.

In the abovementioned problems of the prior art, the UE cannot select oraccess a suitable CSG cell immediately when a suitable CSG cell is foundor subscribed. The communication quality is not optimized.

In addition to the abovementioned problems, the whitelist of the UEpossibly includes a listed CSG cell that is not subscribed by the UE.The related specification does not specify actions of dealing with thewhitelist. Furthermore, the specification specifies no actions for theUE or the network about a situation where the UE camps on the listed CSGcell that is not subscribed. In this situation, the CSG cell can bemisused by the non-subscriber UE.

SUMMARY OF THE INVENTION

The present invention therefore provides a method and related apparatusof controlling CSG cell selection for a wireless communication system tosolve the abovementioned problems.

The present invention discloses a method of controlling CSG cellselection for a wireless communication system including a UE and anetwork. The UE includes a whitelist capable of providing a list ofaccessible CSG cells. The method includes updating the whitelist whenthe UE subscribes to a CSG cell that is not included in the whitelist ordoes not subscribe to a CSG cell in the whitelist.

The present invention further discloses a method of controlling CSG cellselection for a UE of a wireless communication system. The UE comprisesa whitelist providing a list of accessible CSG cells. The methodcomprises periodically searching the CSG cells in the whitelistaccording to a searching period when the UE camps on a macro cell anddoes not meet any of measurement criteria for CSG cell measurement

The present invention further discloses a method of controlling CSG cellselection for a UE of a wireless communication system. The UE comprisesa whitelist capable of providing a list of accessible CSG cells. Themethod comprises performing CSG cell searching when a new CSG cell isadded to the whitelist.

The present invention further discloses a method of controlling CSG cellselection for a UE of a wireless communication system. The UE comprisesa whitelist capable of providing a list of accessible CSG cells. Themethod comprises performing cell selection to select a cell to camp onwhen a CSG cell that the UE currently camps on is removed from thewhitelist

The present invention further discloses a method of controlling CSG cellselection for a UE of a wireless communication system comprising anetwork. The UE includes a whitelist capable of providing a list ofaccessible CSG cells. The method includes receiving a paging messagefrom the network when the UE camps on a CSG cell in the whitelist anddoes not subscribe to the CSG cell, initiating a service requestprocedure when the paging message is received, through the servicerequest procedure receiving a SERVICE REJECT message comprising a rejectcause value from the network, and then searching a cell other than theCSG cell when the reject cause value of the SERVICE REJECT message isreceived.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a wireless communication system.

FIG. 2 is a schematic diagram of a communication device according toembodiments of the present invention.

FIG. 3 is a flowchart of a process according to an embodiment of thepresent invention.

FIG. 4 is a flowchart of a process according to an embodiment of thepresent invention.

FIG. 5 is a flowchart of a process according to an embodiment of thepresent invention.

FIG. 6 is a flowchart of a process according to an embodiment of thepresent invention.

FIG. 7 is a flowchart of a process according to an embodiment of thepresent invention.

FIG. 8 is a flowchart of a process according to an embodiment of thepresent invention.

FIG. 9 is a flowchart of a process according to an embodiment of thepresent invention.

FIG. 10 is a flowchart of a process according to an embodiment of thepresent invention.

DETAILED DESCRIPTION

Please refer to FIG. 1, which is a schematic diagram of a wirelesscommunication system 10. The wireless communication system 10 includes aSystem Architecture Evolution (SAE) core network (CN) 102, a macro cell104, an E-UTRAN (evolved UMTS radio access network) 105 and a userequipments (UE) 106. The macro cell 104 includes CSG (closed subscribergroup) cells 108 and 110. For simplicity, only a UE 106 is shown inFIG. 1. For the UE 106 subscribing CSG services, coverage of the macrocell 104 other than coverage of the CSG cells 108 and 110 is seen asnon-CSG area. Coverage of the CSG cells 108 and 110 is smaller thancoverage of the macro cell 104 and may be home, building, campuscoverage, etc. The SAE CN 102 includes a MME (Mobility ManagementEntity) 110, which is a control plane entity for performingNon-Access-Stratum (NAS) communication with the UE 106 through a radiointerface established between the UE 106 and one or more evolved Node-Bs(e-Node Bs), which is a part of the E-UTRAN 105. For NAS usage about CSGcell selection, the UE 106 stores a whitelist capable of providing alist of CSG cells which the UE 106 is allowed to access. That is, thewhitelist can include a list of CSG cells or nothing, depended onconfiguration sent by the MME 110.

In addition, an attach procedure and a tracking area updating procedureboth initiated by a UE can be used for updating the whitelist.Furthermore, measurement criteria are provided in wireless communicationsystem 10, allowing the UE to reselect a more suitable serving cell whenany of the measurement criteria is met.

Please refer to FIG. 2, which illustrates a schematic diagram of acommunication device 20 according to embodiments of the presentinvention. The communication device 20 can be a UE or a MME shown inFIG. 1 and includes a processor 200, a computer readable recordingmedium 210, a communication interfacing unit 220 and a control unit 230.The computer readable recording medium 210 is any data storage devicethat stores storage data 212, including program code and NAS parameters,and the storage data 212 is thereafter read and processed by theprocessor 200. Examples of the computer readable recording mediuminclude read-only memory (ROM), random-access memory (RAM), CD-ROMs,magnetic tapes, floppy disks, optical data storage devices, and carrierwaves (such as data transmission through the Internet). When thecommunication device 20 is used in the UE, the stored NAS parametersinclude the whitelist. The control unit 230 controls the communicationinterfacing unit 220 and related operations and states of thecommunication device 20 according to processed results of the process200. The communication interfacing unit 220 is responsible forexchanging signals with a peer communication device which represents acommunication device performs functions of a peer communicationprotocol. The communication device 20 can be the UE 106 or the MME 110,and thereby the corresponding communication interfacing unit 220 isrealized by different interfacing device. When the communication device20 is used as the UE 106, the communication interfacing unit 220 is aradio transceiver for wirelessly communicating with the e-Node Bs. Whenthe communication device 20 is used as the MME 110, the communicationinterfacing unit 220 can be an Ethernet networking device exchanging NASsignals with the UE 106 through the e-Node Bs.

Please refer to FIG. 3, which illustrates a flowchart of a process 30according to an embodiment of the present invention. The process 30 isapplied to the NAS functions between a UE (ex. the UE 106) and a network(ex. the MME 110) for controlling CSG cell selection and can be compiledinto the program code of the storage data 212 stored in the computerreadable recording medium 210. The process 30 includes the followingsteps:

Step 300: Start.

Step 302: An MME sends a detach message with a re-attach request to a UEwhen the UE subscribes a CSG cell that is not included in the whitelistof the UE.

Step 304: The UE initiates an attach procedure.

Step 306: Through the attach procedure, the MME sends an ATTACH ACCEPTmessage including an up-to-date whitelist to the UE.

Step 308: The UE replaces the whitelist with the up-to-date whitelist.

Step 310: End.

According to the process 30, the embodiment of the present inventionrequires the MME to send a detach message with a re-attach request tothe UE when the UE subscribes a CSG cell that is not included in thewhitelist of the UE. Then, the UE initiates the attach procedure bysending an ATTACH REQUEST message to the MME. In response to ATTACHREQUEST message, the MME creates the up-to-date whitelist including theoriginal CSG cell list of the UE and the CSG cell that is not includedin the whitelist. The ATTACH ACCEPT message including the up-to-datewhitelist is then sent to the UE. Finally, the UE replaces the whitelistwith the up-to-date whitelist. Therefore, the UE has immediate access tothe CSG cell that is not included in the whitelist of the UE.

Through the process 30, the whitelist is updated when the UE subscribesto the CSG cell that is not included to the whitelist to ensure that theUE obtain the access to the CSG cell.

For example, assume that the UE 106 camping on the macro cell 104subscribes to the CSG cell 108. The CSG cell 110 is mostly suitable forserving the UE 106 but not included in the whitelist of the UE 106.According to the prior art, when the UE 106 subscribes the CSG cell 110,the UE 106 cannot access the CSG cell 110 until access is granted afterthe UE 106 initiates the attach procedure or the tracking area updatingprocedure, possibly causing a great delay. According to the process 30of the present invention, the MME 110, as well as a network, activelyupdates the whitelist of the UE 106 when the UE 106 subscribes the CSGcell 110 with an immediate request for initiation of the attachprocedure or the tracking area updating procedure. Thus, the UE receivesthe access to the CSG cell with less delay.

Please note that, those skills in the art can determine content of theup-to-date whitelist and the way for the UE to include the CSG cell thatis not included in the original whitelist. Taking an example for savingradio resources, the MME can create the up-to-date whitelist onlyincluding the CSG cell that is not included in the whitelist.Accordingly, the UE adds this CSG cell in the up-to-date whitelist tothe original whitelist. Compared to the process 30, transmission of suchan up-to-date whitelist contains less information quantity and thereforesaves more radio resources.

Please refer to FIG. 4, which illustrates a flowchart of a process 40according to an embodiment of the present invention. The process 40 isapplied to the NAS functions between a UE (ex. the UE 106) and a network(ex. the MME 110) for controlling CSG cell selection and can be compiledinto the program code of the storage data 212. The process 40 includesthe following steps:

Step 400: Start.

Step 402: The MME sends a message to the UE to add the CSG cell that isnot included in the whitelist to the whitelist when the UE subscribesthe CSG cell that is not included in the whitelist.

Step 404: End.

According to the process 40, the embodiment of the present inventionrequires the MME to directly send a message to the UE to add the CSGcell that is not included in the whitelist to the whitelist when the UEsubscribes a CSG cell that is not included in the whitelist of the UE.

Preferably, the message is defined in the NAS function of a long termevolution (LTE) wireless system when the UE communicates with theE-UTRAN. Depended on different procedures, the message can be a SMS(shot message service), a CM SERVICE REJECT, a SERVICE REJECT, an ATTACHREJECT, a TRACKING AREA UPDATE REJECT, a ROUTING AREA UPDATE REJECT or aLOCATION UPDATING REJECT message. Please note that the UE can also bethe control of a GSM EDGE radio access network (GERAN) or an UTRAN. Inthis situation, the message is realized with a SMS message.

Instead of updating the whitelist through the attach or tracking areaupdating procedure in the process 30, the MME of the process 40 updatesthe whitelist by directly sending a message. Compared to the process 30,the process 40 brings no interruptions to the services which the UEstill receives when subscribing the CSG cell that is not included in thewhitelist, and also saves more signaling resources.

Please refer to FIG. 5, which illustrates a flowchart of a process 50according to an embodiment of the present invention. The process 50 isapplied to a UE (ex. the UE 106) for controlling CSG cell selection andcan be compiled into the program code of the storage data 212. Theprocess 40 includes the following steps:

Step 500: Start.

Step 502: When subscribing a CSG cell that is not included in thewhitelist, manually add the CSG cell to the whitelist.

Step 504: End.

According to the process 50, the embodiment of the present inventionrequires the UE to update the whitelist by itself when the UE subscribesthe CSG cell that is not included in the whitelist. Instead of relyingon the MME for the whitelist updating in the processes 30 and 40, the UEmanually, actively adds the CSG cell to the whitelist and thus canaccess the CSG cell as soon as possible.

Please refer to FIG. 6, which illustrates a flowchart of a process 60according to an embodiment of the present invention. The process 60 isapplied to a UE (ex. the UE 106) for controlling CSG cell selection andcan be compiled into the program code of the storage data 212. Theprocess 60 includes the following steps:

Step 600: Start.

Step 602: Periodically search the CSG cells in the whitelist accordingto a searching period when the UE camps on a macro cell and doest notmeet any of measurement criteria for CSG cell measurement.

Step 604: End.

According to the process 60, the UE periodically searches the CSG cellsincluded in the whitelist when the UE camps on a non-CSG cell (ex. themacro cell 104) and doest not meet measurement criteria for CSG cellmeasurement.

Preferably, the searching period is configured by a network signalingmessage used for removing all CSG cells listed in the whitelist. Thenetwork signaling message can be an ATTACH ACCEPT message of the attachprocedure or a TRACKING AREA UPDATE ACCEPT message of the tracking areaupdating procedure. A parameter of the searching period is stored in aSIM (Subscriber Identity Module) or a flash memory of the UE if the SIMdoes not support storage of the searching period. When the UE camps onthe GERAN or UTRAN and the parameter of the searching period is storedin the SIM, the searching period is configured by an SMS message. Inpower consumption consideration, the searching period is set to severalminutes, preferably about 5 minutes. In addition, the UE executes theperiodical cell search in background operation and therefore does notimpact the service operation, such as terminal call paging.

With the process 60, the UE can select a subscribed CSG cell with lessdelay. For example, assume that the UE 106 camps on a macro cell 104.According to the prior art, the UE 106 has a chance to reselect the CSGcell 108 as a serving cell only when any of the measurement criteriacapable of triggering cell reselection is met. According to the process60, although none of measurement criteria is met, the UE 106 begins toperiodically search the CSG cells in the whitelist, and thereby canreselect the CSG cell 108 as the serving cell. From the above mentions,the fee of accessing services via a subscribed CSG cell is less thanthat of accessing services via a non CSG cell. In addition, thesubscribed CSG cell can provide better communication quality due to alimited number of UE subscribers. Thus, though the process 60, the UEcan enjoy the service with the better communication quality and lessservice charge.

Please refer to FIG. 7, which illustrates a flowchart of a process 70according to an embodiment of the present invention. The process 70 isapplied to a UE (ex. the UE 106) for controlling CSG cell selection andcan be compiled into the program code of the storage data 212. Theprocess 70 includes the following steps:

Step 700: Start.

Step 702: Perform CSG cell searching when a new CSG cell is added to thewhitelist of the UE.

Step 704: End.

According to the process 70, the UE starts a CSG cell search for the CSGcells included in the whitelist when a new CSG cell is added to thewhitelist. In this situation, the UE can reselect a CSG cell to use evenwhen none of the measurement criteria for CSG cell measurement is met.In addition, the UE stops the CSG cell searching when the CSG cellsearching is done once and the new CSG cell cannot be found.

The CSG cells in the whitelist may not all be subscribed by the UE. Inthis situation, several processes are provided below to prevent the UEfrom misusing the CSG cell which the UE does not subscribe to. Pleaserefer to FIG. 8, which illustrates a flowchart of a process 80 accordingto an embodiment of the present invention. The process 80 is applied toa network for managing a whitelist of a UE and can be compiled into theprogram code of the storage data 212. The process 80 includes thefollowing steps:

Step 800: Start.

Step 802: When the UE does not subscribe to a CSG cell in the whitelist,update the whitelist by removing the CSG cell in the whitelist.

Step 804: End.

According to the process 80, when the UE does not subscribe to the CSGcell in the whitelist, the network updates the whitelist by removing theCSG cell. As a result, the UE does not search the unsubscribed CSG cellwhen next time performing cell search according to the updatedwhitelist.

To remove the CSG cell, preferably, the network first sends a detachmessage with a re-attach request to the UE when the UE does notsubscribe to the CSG cell in the whitelist. In response to the re-attachrequest, the UE initiates an attach procedure. Through the attachprocedure, the network sends an ATTACH ACCEPT message to the UE, and theATTACH ACCEPT message includes an up-to-date whitelist excluding theunsubscribed CSG cell. Finally, the UE removes the CSG cell according tothe up-to-date whitelist.

Another preferred way to remove the CSG cell is described as below. Thenetwork directly sends a message to the UE, and thereby the UE removesthe CSG cell. The message is preferably used in a GERAN, an UTRAN, or aNAS function of SAE for the LTE wireless system or). The message can bea SMS (shot message service), a CM SERVICE REJECT, a SERVICE REJECT, anATTACH REJECT, a TRACKING AREA UPDATE REJECT, a ROUTING AREA UPDATEREJECT or a LOCATION UPDATING REJECT message.

In addition to the process 80, the CSG cell can also be manually removedfrom the whitelist when the UE does not subscribe to the CSG cell in thewhitelist.

The embodiment of the present invention further provides processes forthe UE when the unsubscribed CSG cell is removed from the whitelist.Please refer to FIG. 9, which illustrates a flowchart of a process 90according to an embodiment of the present invention. The process 90 isapplied to a UE for controlling CSG cell selection corresponding to awhitelist of the UE and can be compiled into the program code of thestorage data 212. The process 90 includes the following steps:

Step 900: Start.

Step 902: Perform cell selection to select a cell to camp on when a CSGcell that the UE currently camps on is removed from the whitelist.

Step 904: End.

According to the process 90, the UE performs cell selection to select anew cell to camp on when the currently-camped CSG cell is removed fromthe whitelist. The selected cell is never the currently-camped CSG celland can be a CSG or normal cell. Through the process 90, the UE activelyselects another cell to camp on when the currently camped CSG cell isremoved from the whitelist.

Please refer to FIG. 10, which illustrates a flowchart of a process 1000according to an embodiment of the present invention. The process 1000 isutilized for a UE and a network to control CSG cell selectioncorresponding to a whitelist of the UE and can be compiled into theprogram code of the storage data 212. The process 1000 includes thefollowing steps:

Step 1002: Start.

Step 1004: The network sends a paging message to the UE when the UEcamps on a CSG cell in the whitelist and does not subscribe to the CSGcell.

Step 1006: The UE initiates a service request procedure when receivingthe paging message.

Step 1008: Through the service request procedure, the network sends aSERVICE REJECT message including a reject cause value to the UE.

Step 1010: The UE searches a cell other than the CSG cell when receivingthe reject cause value of the SERVICE REJECT message.

Step 1012: End.

According to the process 1000, when the UE does not subscribe to thecurrently camped CSG cell, the network sends the paging message. Whenreceiving the paging message, the UE initiates the service requestprocedure where the network sends the SERVICE REJECT message includingthe reject cause value utilized for triggering the UE to search the cellother than the currently camped CSG cell. Thus, through the process1000, the network can actively require the UE to search another cell tocamp on when the UE does not subscribe to the currently camped CSG cell.

Preferably, the searched cell is a CSG cell or a normal cell. The rejectcause value is 15. The currently camped CSG cell and the searched cellbelong to different defined area in the same or different PLMN. Thedefined area can be a routing area, a tracking area, or a location area.In this situation, when the cell in another routing, tracking, orlocation area is searched and found, the UE accordingly initiates atracking, a routing, or a location update procedure. Through theprocedure initiated by the UE, the network sends a TRACKING AREA UPDATEACCEPT, a ROUTING AREA UPDATE ACCEPT, or a LOCATION UPDATING ACCEPTmessage to the UE. Any of the messages include an up-to-date whitelistexcluding the CSG cell in the whitelist so that the UE removes thecurrently camped CSG cell from the whitelist according to the up-to-datewhitelist.

In a special case where the searched cell belong to another locationarea of the GERAN or the UTRAN in the different or same PLMN as thecurrently camped CSG cell, the UE initiates the location or the routingarea update procedure instead of any of the three types of area updateprocedures. In this situation, the network sends the ROUTING AREA UPDATEACCEPT or a LOCATION UPDATE ACCEPT message according to the initiatedprocess to trigger the UE to the currently camped CSG cell from thewhitelist.

Thus, the process 1000 specifies the UE to move to another cell andremoves the currently-camped CSG cell from the whitelist when thecurrently-camped CSG cell is included in the whitelist and notsubscribed by the UE.

The processes 30-50 solve the first problems of the prior art by meansof the fast update of the whitelist. The processes 60 and 70 solve thesecond problems of the prior art by means of periodical cell searchingand cell searching in response to the whitelist update respectively. Theprocesses 80-90, 1000 provides actions for the UE to deal with asituation where the UE camps on an unsubscribed CSG cell, and a relatedsituation where the currently camped CSG cell is removed from thewhitelist.

In conclusion, the embodiments of the present invention improve the CSGcell selection for the UE and avoid possible system errors.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention.

What is claimed is:
 1. A method of controlling closed subscriber group,hereinafter called CSG, cell selection for a user equipment, hereinaftercalled UE, used in a wireless communication system comprising a network,the UE comprising a whitelist capable of providing a list of accessibleCSG cells, the method comprising: updating the whitelist when the UEsubscribes to a CSG cell that is not included in the whitelist or doesnot subscribe to a CSG cell in the whitelist, wherein updating thewhitelist comprises: receiving a first message from the network; andadding the CSG cell not included in the whitelist to the whitelistaccording to the first message when the UE subscribes to the CSG cellnot included in the whitelist, or removing the CSG cell from thewhitelist according to the first message when the UE does not subscribeto the CSG cell in the whitelist.
 2. The method of claim 1, wherein theCSG cell is manually added to the whitelist or manually removed from thewhitelist.
 3. The method of claim 1, wherein the first message is anATTACH ACCEPT message comprising an up-to-date whitelist comprising theCSG cell that is not included in the whitelist, and the ATTACH ACCEPTmessage is received through an attach procedure initiated by the UE inresponse to a re-attach request sent from the network.
 4. The method ofclaim 1, wherein the first message is a short message service (SMS)message, CM SERVICE REJECT message, a SERVICE REJECT message, a ATTACHREJECT message, a TRACKING AREA UPDATE REJECT message, a ROUTING AREAUPDATE REJECT message or a LOCATION UPDATING REJECT message.
 5. Themethod of claim 1, wherein the first message is an ATTACH ACCEPT messagecomprising an up-to-date whitelist excluding the CSG cell to be removed,and the ATTACH ACCEPT message is received through an attach procedureinitiated by the UE in response to a re-attach request sent from thenetwork.
 6. A method of controlling CSG (Closed Subscriber Group) cellselection for a user equipment of a wireless communication system, theuser equipment (UE) comprising a whitelist capable of providing a listof accessible CSG cells, the method comprising: performing CSG cellsearching when a new CSG cell is added to the whitelist, such that theUE is able to reselect the new CSG cell even though none of cellreselection criteria for the new CSG cell measurement is met or none ofmeasurement criteria for the new CSG cell measurement is met.
 7. Themethod of claim 6 further comprising stopping the CSG cell searchingwhen the CSG cell searching is done once and the CSG cell cannot befound.
 8. A method of controlling CSG (closed subscriber group) cellselection for a user equipment, hereinafter called UE, used in awireless communication system with a network, the UE comprising awhitelist capable of providing a list of accessible CSG cells, themethod comprising: receiving a paging message from the network when theUE camps on a CSG cell in the whitelist and does not subscribe to theCSG cell; initiating a service request procedure when the paging messageis received; through the service request procedure, receiving a SERVICEREJECT message comprising a reject cause value from the network; andsearching a cell other than the CSG cell when the reject cause value ofthe SERVICE REJECT message is received.
 9. The method of claim 8,wherein the CSG cell belongs to a first defined area, and the UEsearching the cell other than the CSG cell when the reject cause valueof the SERVICE REJECT message is received comprises: searching the cellin a second defined area.
 10. The method of claim 9 further comprising:initiating an area update procedure when the cell in the second definedarea is searched and found; through the area update procedure, receivinga first message from the network, the first message comprises anup-to-date whitelist excluding the CSG cell in the whitelist; andremoving the CSG cell from the whitelist according to the up-to-datewhitelist.
 11. The method of claim 10, wherein the first defined area isa tracking area, a routing area or a location area, the second definedarea is a tracking area, a routing area or a location area, the areaupdate procedure is a tracking area update procedure, a location areaupdate procedure or a routing area update procedure, and the firstmessage is a TRACKING AREA UPDATE ACCEPT message, a LOCATION UPDATINGACCEPT message, or a ROUTING AREA UPDATE ACCEPT message.
 12. The methodof claim 10, wherein the second defined area is a location area of aGSM/EDEG radio access network or a UMTS radio access network in a samepublic land mobile network as the first defined area, the area updateprocedure is a location area update procedure or a routing area updateprocedure, and the first message is a LOCATION UPDATE ACCEPT message ora ROUTING AREA UPDATE ACCEPT message.
 13. A method of controlling closedsubscriber group, CSG, cell selection for a network of a wirelesscommunication system, the method comprising: sending a paging message toa user equipment, UE, of the wireless communication system, the UEcomprising a whitelist capable of providing a list of accessible CSGcells, wherein the UE camps on a CSG cell in the whitelist and does notsubscribe to this CSG cell; and sending a SERVICE REJECT messageincluding a reject cause value to the UE when UE initiates a SERVICEREQUEST procedure in response to the paging message, such that the UEhas to search a cell other than the currently camped CSG cell when thereject cause value of the SERVICE REJECT message is received by the UE.